The present invention relates to cable-supported platforms used in dry dock ship repair and for other purposes.
Although as explained below the present invention is not limited to such an application, one important application of the invention is in dry dock ship repair. In this regard, repairs in dry dock on the bow or stern of a ship and, in some instances, on the sides of a ship, present particular difficulties and both the bow and stern are inefficient to access using conventional xe2x80x9cstick-builtxe2x80x9d scaffolding methods. For example, the time taken, and personnel needed, to assemble a single, fixed tower of sufficient height (80 feet) relative to the bow of a ship are quite substantial (on the order of 64 person-hours total).
Other important considerations in providing a workable, efficient support platform system for such an application include the need to provide attachment of the support platform system to a dry dock for ship repair with minimal modifications of the dry dock. Further, set-up and calibration of the system should be simple. In addition, it would be advantageous to be able to access exterior ship hull surfaces without the use of overhead support structures or scaffolding.
A traditional xe2x80x9cStewart Platformxe2x80x9d cable configuration with overhead support points has a number of important advantages but does not allow access to some work sites such as a ship bow or stern. Exploring this point in more detail, the basic, six cable Stewart Platform is shown in schematic form in FIG. 1 wherein six cables, denoted C1 to C6, are connected between attachment or suspension points A1, A2 and A3 forming an upper or base triangle. A workpiece or moving platform P is supported by cables C1 to C6. A platform edge, identified as PE, is supported by an associated suspension point A1. An important advantage of this configuration of cables C1 to C6 is that the configuration can control suspended loads, tools, equipment and the like in all six degrees of freedom with sway or rotations. Further, a spine (not shown) can be integrated between the platform P and the support structure to provide tension in all six cables C1-C6 outside of the typical gravity-forced platform work volume. In other words, rather than hanging directly from the upper support points A1-A3 down into a position dictated by gravity, the platform can be pushed to the side using such a spine. The prior art systems include control arrangement which provides control of each of cables C1-C6 using a winch and is powered by a power amplifier. A computer is used to determine the amount of motion that the winch is to undergo to provide the desired cable control, based on sensor inputs. Joystick commands or other computer algorithm commands supplied to the winches can be used to provide complex platform movements which can be controlled throughout the work volume. Pre-programmed platform trajectories allow the operator to pre-plan movements with updated movement path information based on interaction with the environment. For example, the platform can be caused to maneuver around an obstacle placed in the pre-programmed movement path of the platform. Thus, Stewart Platform cable configurations possess a number of features but are limited insofar as providing access to some work sites.
Patents of interest here include the following, the subject matter of which is hereby incorporated by reference: U.S. Pat. No. 2,164,128 (Medenwald); U.S. Pat. No. 4,666,362 (Landsberger, et al.); U.S. Pat. No. 4,883,184 (Albus); and U.S. Pat. No. 5,585,707 (Thompson et al.). Briefly considering the three patents, the Medenwald patent discloses a basic Stewart Platform including a parallel-link manipulator configuration of six cables attached to a crane, with a single winch of the crane used as the lift device for all six cables. The cables stabilize attached loads in six degrees of freedom.
The Landsberger et al. patent discloses a Stewart Platform, parallel-link manipulator of six cables attached in a xe2x80x9ctripodxe2x80x9d configuration, including a telescoping support spine for the moving platform. Hydraulic power and hydraulic motors are used. The lengths of the cables are independently controlled through the use of power-spools.
The Albus patent discloses a cable and lifting platform of the Stewart Platform type which is used for stabilized load lifting. Load imbalance relative to the center of mass of the platform is sensed and the load is repositioned to control the imbalance. The cables stabilize the attached load in six degrees of freedom.
The Thompson et al. patent discloses a cable-driven Stewart Platform system, which is suspended from above, and also tensioned from below. Platform movement in six degrees of freedom is provided and the central system includes on-board winches, position sensing, optical sensing of tension, and a controller for these functions.
In accordance with the invention, a platform system is provided which affords a number of important advantages over prior art systems including the Stewart Platform system, and the variations thereon, discussed hereinbefore. As will become more apparent from the discussion below, the present invention enables attachment to a dry dock for use in ship repair with minimum modifications of the dry dock. Further, the system of the invention is simple to set up and to calibrate. In addition, the system of the invention permits accessing of the exterior surfaces of a ship""s hull without the need for overhead support structures or scaffolding. Further, the system of the invention enables suspending of a moving platform for carrying workers, tools and equipment, and/or materials to a repair or conversion site, by providing intuitive control through the use of a hand-winch or joystick manual or computer control, throughout a large work volume.
According to the invention, there is provided a cabled platform suspension system comprising:
a platform including means defining first and second support points at spaced locations along a front work-access edge of the platform and a third, stabilizing/rotator support point;
a support structure for the platform defining first, second, third and fourth suspension points arranged in a substantially rectangular pattern and from which the platform is suspended; and
at least six cables connected between the platform and the support structure, the six cables comprising:
first and second cables respectively connected between the first and fourth suspension points and the first and second support points on the platform;
third and fourth cables respectively connected between the second and third suspension points and the first and second support points on the platform; and
fifth and sixth cables connected between the second and third suspension points and the third support point on the platform.
In one preferred embodiment, the platform includes first and second laterally and oppositely extending support members and the first and second support points are located at respective distal ends of the support members. Advantageously, the platform further includes a rearwardly extending support member having a distal end and the third support point is located at the distal end of said rearwardly extending support member. Preferably, the platform comprises a platform member and the rearwardly extending support member comprises a centrally disposed support strut affixed to a rear edge of the platform member and first and second tie elements extending between the distal end of the support strut and the rear edge of the platform member on opposite sides of the support strut.
In accordance with a preferred implementation, the suspension points are respectively located on the towers of a dry dock facility.
In a further preferred embodiment, the platform comprises a V-shaped platform member having a central portion and first and second angled leg portions and including a support strut extending rearwardly of the central portion and having a distal end, the first and second support points being respectively located at distal ends of the leg portions and the third support point being located at the distal end of the support strut. Advantageously, the platform further comprises a downwardly depending element affixed to the distal end of the support strut and first and second tie members connected between the element and the distal ends of the leg portions.
In yet another preferred embodiment, the platform includes a main platform and an elevator sub-platform movable, in use, between a ground location and a position on the main platform.
In a further advantageous embodiment, the platform includes a platform member, a centrally disposed, downwardly depending truss member and a plurality of tie elements connected between the truss member and distal ends of the platform member.
In an advantageous implementation, the platform comprises a platform member of a modular construction. Preferably the platform member comprises a plurality of separate, removable platform sections.
Advantageously, the platform member comprises a corrugated sub-deck.
The cabled platform suspension system preferably comprises control means for controlling the cables to provide manipulation of the platform through a defined work volume, the control means including a tension sensor for each cable for sensing the cable tension on the associated cable. Advantageously, the system further comprises a pulley for each cable, each of the tension sensors being disposed between a portion of said platform and the associated pulley. Preferably, the system further comprises a winch for each cable, each of the cables extending from the associated winch through the associated pulley to the corresponding support point on the platform. The control means preferably further comprises a motor including a rotating motor shaft for driving each of the winches and at least one of a position sensor, an encoder and a tachometer for monitoring a parameter associated with rotation of the motor shaft and means for controlling the associated winch in accordance with that parameter.
Preferably, the system further comprises magnetic means for securing the platform to at least one work site surface to stabilize platform positioning. Advantageously, the magnetic means comprises a plurality of movable electromagnets.
The system preferably further comprises control means for controlling the cables so as to manipulate the platform throughout a defined work space, wherein the control means including a joystick controller comprising a base, a movable plate member simulating the platform and six linear potentiometers connected between said base and said movable member in manner replicating the connections between said six cables and said support points and said suspension points. Preferably, the control means further comprises a winch for each of the six cables, a power amplifier, associated with each linear potentiometer and each winch, for receiving a control signal from a corresponding one of linear potentiometers and for, based on that control signal, producing a further control signal for controlling operation of the associated winch.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.